It has long been desired to produce nonwoven fabrics that combine the low cost of nonwoven manufacturing process with the durability of traditional knit and woven textiles to multiple uses and repeated launderings. However, to date, expedients that have been proposed for increasing the durability of nonwoven fabrics have achieved only partial success in terms of performance enhancements. Further, such approaches have been costly and have resulted in detrimental effects on tactile and drape properties, to render the modified fabrics no longer suitable for their intended end use.
The use of open mesh nets, or scrims, has been proposed in the past for altering certain physical characteristics of nonwoven fabrics, such as tensile strength and durability. Scrims are produced by numerous methods including weaving, extrusion casting, cross-laying threads or filaments and bonding at their intersections. U.S. Pat. Nos. 4,775,579; 5,334,446; 5,393,599; 5,431,991; and 5,874,159 all disclose nonwoven fabrics having an open mesh net member incorporated therein. A scrim layer is typically bonded between fibrous layers to form a nonwoven product to suit a particular application. Scrim layers have been proposed as a stiffener, for strengthening reinforcement, to make non-elastic or highly elastic products; and for a variety of other purposes.
Many different expedients have been proposed for bonding a scrim layer into a multi-layer nonwoven product. Thermal bonding, adhesive bonding, stitch bonding, and high-pressure water jet entanglement are typical methods for constructing scrim reinforces laminates. None of these expedients has been completely successful. Adhesive bonding involves specialized equipment, adds a processing step, and adhesive itself is expensive. Thermal bonding results in stiffening of the fabric due to the stiffness of the bond points themselves, which results in an undesirable tactile quality in many durable good end uses. Stitch bonding, while aesthetically pleasing, is slow by comparison to most other nonwoven bonding methods and includes the cost of expensive yarns, thereby negating the economic benefits of the original nonwoven substrate. Bonding by high-pressure water jets typically requires the use of layers of unbonded staple fibers to conceal the scrim as an interior layer in the fabric. Hydroentangled staple layers tend to lack the type of durability and pill resistance required for highly durable, multi-use fabrics without the inclusion of expensive finishes, which also add cost and have negative effects on hand and drape.
Thus, there remains an unfilled need for the production of a highly durable nonwoven product with the high strength performance that can be reliably and economically manufactured.
The present invention comprises a composite nonwoven fabric based on a multi-layered construction utilizing a scrim as an interior strength bearing member with nonwoven fabrics as the outer layers of a fabric that may be first consolidated by the use of high pressure water jets and then imaged using water jets and a three dimensional forming surface.
In accordance with one aspect of the present invention the scrim layer is positioned between a thermally point-bonded nonwoven substrate fabric formed of polymeric staple length fibers or essentially continuous filaments, and a secondary substrate fabrics of entangled polymeric staple length fibers or essentially continuous filaments. This precursor composite is then directed to an imaging device which is subjected to the action of high pressure water jets to consolidate the layers of the precursor composite to one another and to impart an image therein corresponding to the image of the imaging device. U.S. Pat. Nos. 5,882,883 and 5,827,597 disclose processes and equipment that are suitable for use in forming imaged laminated nonwoven fabrics of the present invention, and such patents are hereby incorporated herein in their entireties by this reference.
The reliance upon a thermally point bonded nonwoven substrate as one of the layers of the composite contributes to the abrasion resistance and overall durability of the composite fabric. The inclusion of an entangled fabric of predominantly staple length fibers provides added bulk, coverage, and imparts a good hand to the composite fabric. The resulting composite construction offers excellent strength, uniformity, opacity, durability and aesthetic properties in a nonwoven fabric.
In accordance with another aspect of the present invention, prior to imaging, the entangled nonwoven substrate layer is comprised of staple length fibers or continuous filaments that are held together by knotting or mechanical friction as a result of needling or water jet entangling. Such fabrics are produced, for example, by cross-lapping a carded fibrous layer of randomized 0.8 to 3.5 denier staple length fibers. The carded web is subsequently entangled using commercial processes, most preferentially hydroentanglement systems, as exemplified by Perfojet Jetlace 2000 or Fleissner Aquajet system. When continuous filament fabrics are used, thermoplastic continuous filaments of 0.8 to 3.5 denier, comprised of thermoplastic polymers such as polyester, polyamide, polypropylene or polyethylene, are preferred. Such fibrous layers have a basis weight in the range of 15 to 100 grams per square meter (gsm). Various prior art patents disclose techniques for manufacturing nonwoven fabrics by hydroentanglement of staple length fibers, including U.S. Pat. No. 3,485,706, the disclosure of which is hereby incorporated herein by this reference. While having achieved substantial commercial success, it is well known that such fabrics have relatively low tensile strength and poor elongation properties. However, it has been discovered that when such fabrics are incorporated into a composite that includes a scrim reinforcing layer, and a thermally point-bonded layer, and that composite is imaged by the high pressure water jets, the physical properties of the resulting laminate are greatly enhanced.
In accordance with another aspect of the invention, the thermally point-bonded fabric performs a number of functions; to increase the basis weight of the composite fabric, to bond the entangled fibrous layer to the scrim, and to further conceal the interior scrim layer. As the coarseness of the scrim increases, correspondingly, the basis weight of the thermal bond layer will be increased. Basis weights in the range of 20 to 100 gsm are generally sufficient to bond the substrate layers of the composite fabric and to mask the internal scrim layer. Suitable deniers for the fibers or filaments are in the range of 0.8 to 4.0.
The thermally bonded substrate layer is produced on a conventional manufacturing line, such as a card line or spunbond line as is well known. The consolidation step in the process may be any of the known methods of thermal bonding, including through-air bonding and thermal point bonding, with the latter being most preferred. The degree of bonding in such commercial processes is generally sufficient to provide the strength and durability required by the intended end use, as well as that required by the intermediate operations, such as winding, slitting and other converting steps. In accordance with the present invention, the degree of bonding must be such that the fabric can be processed through the required intermediate steps but labile enough to break under the action of the high-pressure water jets. This is required so that the fibers or filaments entangle with the fibers of the entangled fibrous layer by extending through the scrim layer. This is achieved during the imaging step and serves to consolidate the layers of the composite while producing the final desired aesthetics of the fabric of the invention.
The present invention contemplates that different forms of scrim materials may be used, depending on the anticipated end use of the laminated nonwoven fabric. The stiffness of the composite can be controlled by the properties of the scrim layer where a heavy, coarse polypropylene scrim will produce a stiff composite fabric. Metallic scrims produce composite fabrics that have substantial bending memory and high electrical conductivity. Cast lightweight polyester scrims can be used to produce non-elastic imaged products suitable for jet dyeing. Elastic scrims can be used when some degree of stretch and recovery is desired in the final fabric. The required fabric properties for a given end use application will be considered when selecting the type of scrim used in the composite fabric designs of the present invention.
The above description sets forth rather broadly the more important features of the present invention so that the detailed description that follows may be better understood, and so that the present contributions to the art my be better appreciated. It is to be understood that there are additional features of the disclosure that will be described hereinafter which will form the subject matter of the claims appended hereto. In this respect, before explaining the several embodiments of the disclosure in detail, it is to be understood that the disclosure is not limited in its application to the details of the construction and the arrangements set forth in the following description or illustrated drawings. The present invention is capable of other embodiments, of being practiced, and carried out in various ways, as will be appreciated by those skilled in the art. In addition, it is to be understood that the phraseology and terminology employed herein are for description and not limitation.